The present invention relates to the use of a highly oxidizing composition for detecting any contaminants on a surface with organic substances.
Detergents and disinfectants that contain strong oxidants have been known for a long time Such compositions are described in various prior art patents. European Patent No. EP 1,343,864 B1 discloses a detergent and disinfectant containing a water-soluble permanganate, which additionally includes a pH adjusting agent for securing an alkaline milieu of at least pH 10, preferably at least pH 12, such as NaOH, for example, as well as at least one other oxidant having an oxidative potential higher than that of manganese(VII) to manganese(VI), and preferably above that of HO2− to OH−, preferably a pemxydisulfate.
Such a composition will unfold its oxidative effect in a highly alkaline milieu predominantly by reducing Mn(VII) to Mn(VI), whereby the latter will be simultaneously oxidized to oxalate if organic carbon is present. The other oxidant having an oxidative potential higher than that of manganese(VII), such as one or more alkali metal peroxydisulfates, for example, will react more slowly with organic carbon as a permanganate, such that, upon dissolution of the powdery composition in water, there will first be oxidation of hydroxide ions to hydrogen peroxide ions due to both the peroxydisulfate and the permanganate, which is reduced to Mn(VI) in the process. See the following Equations 1 and 2:3OH−+S2O82−→HO2−+2SO42−+H2O  Equation 14OH−+4MnO4−→O2↑+4MnO42−+2H2O  Equation 2The resulting hydrogen peroxide ion may, however, cause re-oxidation of Mn(VI) to Mn(VII).HO2−+2MnO42−+H2O→3OH−+2MnO4−  Equation 3
When the disintegration rate of the peroxydisulfate cannot catch up with that of the permanganate (e.g. because disintegration of the permanganate is favored by high concentration and/or good oxidability), increased formation of Mn(VI) will occur. The predominance of the hexavalent manganese species results in a green color of the solution as opposed to the initial purple coloration due to Mn(VII). The oxidation of organic compounds (here referred to as “CH2O” in representation of the oxidation step ±0 and in particular of carbohydrates) to oxalate by Mn(VII) and the associated reduction of the permanganate is quick in any case, as the high pH has an anionizing effect on numerous organic materials, facilitating targeting of anionic oxidants. The oxidation of organic substances by Mn(VII) also involves MnO43−, in which manganese having the atomic number +5 is present (Equation 4) but may be re-oxidized to hexavalent manganese by permanganate (Equation 5):2{CH2O}+3MnO4−+2H2O→C2O42−+3MnO43−+8H+  Equation 4MnO43−+MnO4−→2MnO42−  Equation 5
Targeting organic substances with permanganate according to Equation 4, however, does not require the high efficacy of such a combination of permanganate and peroxydisulfate. Instead, quick and efficient oxidation of organic materials is caused by now starting radical reactions. Their starting point are SO4− radicals that may result from the peroxydisulfate by hemolytic cleavage of peroxydisulfate (Equation 6) or by reacting the same with organic compounds (Equation 7) (herein, compounds in bold indicate radicals or radical ions):S2O82−→2SO4−  Equation 62S2O82−+2{CH2O}+2H2O→2SO42−+2SO4−+{C+1—R}+4H+  Equation 7in which {C+1—R} represents a radical with carbon in oxidation step +1, such as formally {H2C2O3}2−, in which there is a double bond between the carbon atoms.
Primarily, however, sulfate radicals seem to be generated by reacting Mn(V) (see equation 4 above) with peroxydisulfate (Equation 8):MnO43−+S2O82−→MnO42−+SO42−+SO4−  Equation 8
In the process, Mn(V) is re-oxidized to Mn(VI). Eventually, based on the thermodynamic instability of Mn(VI), predominantly Mn(II) is formed:MnO42−+H2O→O2↑+HMnO2−+OH−  Equation 9
The Mn(II) causes the composition to have a yellow color. Such a color can also be interpreted as an indication that the oxidants were consumed by large amounts of contaminants. Mn(II) is slowly oxidized to Mn(IV) by atmospheric oxygen, and the Mn(IV) can eventually sediment in the form of manganese dioxide (MnO2).
Combinations of permanganate and peroxydisulfate therefore display a synergistic effect in oxidizing organic carbon and at the same time provide an indication system, as the initially purple solution assumes an easily visible green color in the presence of organic carbon. As possible alternatives to peroxydisulfate, periodate, peroxydiphosphate, ozone and hypochlorite are mentioned.
According to European Patent No. EP 1,343,864 B1, the detergent and disinfectant can be used for cleaning drinks dispensing apparatuses (by flushing the apparatus with the aqueous solutions) or contaminated bottles from organic residues or for cleaning surfaces in vegetable processing plants or breweries, albeit in the latter case for removing inorganic plaque—after the agent has acted on the plaque “for less than one hour”.
An improvement of the detergent and disinfectant is disclosed in European Patent No. EP 1,730,258 B1, in which pH buffering substances, preferably alkali metal (hydrogen) carbonates as well as anti-oxidant polyphosphates are added.
In European Patent No. EP 1,456,338 B1, combinations of water-soluble chlorite and bromate, which are also stabilized using a pH regulator at a highly alkaline pH to suppress the formation of chlorine dioxide, are disclosed. As applications, again drinks dispensing apparatuses, as well as pipelines in the dairy and beverage industries, as well as the processing of swimming pool water are mentioned.
A drawback of these prior-art detergents is that the aqueous solutions are mostly only 1-3% solutions of the contained oxidant. While these solutions are perfectly well usable in containers or conduits, they quickly drain off surfaces when the surface is not an exact horizontal plane, best with an elevated boundary. Particularly in the case of smooth stainless steel surfaces or ceramic tiles, as they are commonly used in the beverage or food industries, reliably cleaning surfaces is impossible, especially when they are tilted or vertical surfaces. Another drawback is manganese dioxide formation, as manganese dioxide is not soluble in water and therefore hardly removable using the means described above.
It is an aim of the present invention to overcome these drawbacks. Another aim of the invention is to develop a method enabling visual control of the degree of contamination of industrial surfaces.